A multi-tube heat exchanger 12 shown in FIGS. 1, 2 are often used if a high degree of heat exchanging performance is required like the case described above.
That is, multiple inner tubes (heat transmitting tubes) group 14 which the first fluid (high-temperature gas) passes through and an outer tube (body) 16 which the second fluid (cooling water) passes through are provided. Both ends of each of the multiple heat transmitting tubes (heat transmitting tubes) 14, 14, . . . are held and disposed on introduction side/discharge side holding plates 18, 20 located on the first fluid introduction side and first fluid discharge side. In the indicated example, the multiple heat transmitting tubes 14, 14 . . . are disposed within the body 16 via introduction side/discharge side holding plates (tube sheet) 18, 20 located on both sides of the body 16. The both ends of the body 16 have introduction/discharge ports (connection pipes) 26, 28 with flanges 26a, 28a via conical introduction side/discharge side rectifying cylinders (rectifying portions) 22, 24 of truncated cone shape, so that the first fluid (high-temperature gas) can pass through the heat transmitting tubes 14, 14 . . . The body 16 has introduction/discharge nozzles 30, 32 on its top and bottom faces for the second fluid (cooling water) to be capable of passing outside each heat transmitting tube 14.
However, in the multi-tube heat exchanger 12 shown in FIGS. 1, 2, if the quantity of its heat transmitting tubes 14 is increased so as to increase heat exchanging efficiency, flow resistance of cooling water is increased or gas flow velocity is decreased and heat transfer rate drops accompanied thereby, so that consequently, increasing of heat exchanging efficiency is difficult.
Further, the above-mentioned multi-tube heat exchanger 12 needs a number of production steps and its weight tends to be increased.
The inventors of the present invention have proposed a multi-tube heat exchanger having a structure described below (Japanese Patent Application No. 2000-061541: Japanese Patent Application No. 2001-24890; being not published on the priority date) in order to provide a multi-tube heat exchanger capable of increasing heat exchanging efficiency easily and additionally decreasing the number of manufacturing steps.
“Multi-tube heat exchanger containing multiple heat transmitting tubes disposed inside the body characterized in that each of the respective heat transmitting tubes is comprised of a heat transmitting tube main body having a flat section and a number of heat transmitting fins connecting between opposing faces in the length direction of the heat transmitting tube main bodies.”
However, in case where the heat transmitting fins having the above-described structure are formed, pollutant (soot, oily stain and the like) is likely to adhere to heat transmitting wall faces and in an extreme case, clogging occurs partially due to pollutant, thereby indicating that a large drop in heat exchanging efficiency (heat exchanging performance) is likely to occur.